The use of a lead-acid battery is classified into trickle use (float use) in which the battery usually charges on fixed voltage and discharges as needed and cycle use in which the battery charges and discharges repeatedly. The main cause of deterioration of the lead-acid battery in the former trickle use is the corrosion of a positive-electrode grid. This is because the alloy of the grain boundary used for a grid material is selectively corroded during charge.
Using the grid into which the pure lead sheet was processed was proposed by U.S. Pat. No. 3,862,861.
Since the grain boundary of pure lead is not clear, the above-mentioned problem due to the grain boundary does not occur and an excellent trickle life performance can be obtained. However, when pure lead is used for a grid, in cycle use, it has a defect in that the capacity does not recover even if it charges, especially when deep discharge occurs.
As this provision, the method of making a lead-tin alloy instead of a pure lead into the shape of a sheet with rolling, and using the grid obtained by punching-processing or expanded processing was proposed by U.S. Pat. No. 5,120,620. Although the charge acceptance characteristics after deep charge can be improved by this method, since the metal used for said grid is a lead-tin alloy, a grain boundary exists, the corrosion of a positive-electrode grid advances in a trickle life, and there is a problem which is a short life compared with a pure lead grid.